forms.py

from django import forms
from django.contrib.auth.models import User
from django.utils.translation import ugettext_lazy as _
from registration.forms import RegistrationForm


class SniptRegistrationForm(RegistrationForm):
    """
    Subclass of ``RegistrationForm`` which enforces uniqueness of
    email addresses and further restricts usernames.
    """

    def clean_username(self):
        """
        Validate that the username is alphanumeric and is not already
        in use.
        """
        existing = User.objects.filter(username__iexact=self.cleaned_data["username"])
        if existing.exists():
            raise forms.ValidationError(_("A user with that username already exists."))

        elif "@" in self.cleaned_data["username"]:
            raise forms.ValidationError(_("Cannot have '@' in username."))
        elif "." in self.cleaned_data["username"]:
            raise forms.ValidationError(_("Cannot have '.' in username."))
        elif "+" in self.cleaned_data["username"]:
            raise forms.ValidationError(_("Cannot have '+' in username."))

        else:
            return self.cleaned_data["username"]

    def clean_email(self):
        """
        Validate that the supplied email address is unique for the
        site.
        """
        if User.objects.filter(email__iexact=self.cleaned_data["email"]):
            raise forms.ValidationError(
                _(
                    """This email address is already in use. Please supply a
                     different email address."""
                )
            )
        return self.cleaned_data["email"]